chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g...

71

Transcript of chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g...

Page 1: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 2: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 3: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 4: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 5: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 6: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 7: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 8: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 9: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 10: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 11: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 12: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 13: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 14: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 15: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 16: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 17: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 18: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 19: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 20: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 21: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 22: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 23: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 24: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 25: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 26: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 27: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 28: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 29: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 30: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 31: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 32: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 33: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 34: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 35: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 36: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 37: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 38: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 39: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 40: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 41: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 42: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 43: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 44: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 45: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 46: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 47: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 48: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 49: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 50: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 51: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 52: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 53: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 54: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 55: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 56: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 57: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 58: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 59: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 60: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 61: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 62: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 63: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 64: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 65: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 66: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 67: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 68: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 69: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 70: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se
Page 71: chimie12.weebly.comchimie12.weebly.com/.../6/12264090/vasile-sorohan-culegere-chimie.pdf · 294,3 g apå si se tyrrneazá 0 solutie de determine cantitateade halogenû:rä 14. Se

chimie12.weebly.comchimie12.weebly.com/uploads/1/2/2/6/12264090/culegere-probleme-chimie-vii.pdf · 600g &stilatž ca in \£ntru in 2.17. In ce raport cu o solutic! de ù¿-sntitàÿ

chimie12.weebly.comchimie12.weebly.com/uploads/1/2/2/6/12264090/culegere-probleme-chimie-vii.pdf · 600g &stilatž ca in \£ntru in 2.17. In ce raport cu o solutic! de ù¿-sntitàÿ

Descătuşări – Fărâme de azimă - versuri vechi şi noi -€¦ ·  · 2011-12-06Consilier editorial: prof. dr. Monica Grosu Lector de carte: prof. drd. Adina Voica Sorohan

Descătuşări – Fărâme de azimă - versuri vechi şi noi -€¦ ·  · 2011-12-06Consilier editorial: prof. dr. Monica Grosu Lector de carte: prof. drd. Adina Voica Sorohan

Chimia - prietena mea - ccdmures.roccdmures.ro/cmsmadesimple/uploads/file/rev6/chimie.pdf · expoziţia de produse cosmetice bio. Am dorit să aducem cercului de chimie o notă de

Chimia - prietena mea - ccdmures.roccdmures.ro/cmsmadesimple/uploads/file/rev6/chimie.pdf · expoziţia de produse cosmetice bio. Am dorit să aducem cercului de chimie o notă de

l19_Violeta Georgescu, Mardarie Sorohan - Fizica Moleculara_RO

l19_Violeta Georgescu, Mardarie Sorohan - Fizica Moleculara_RO

PDF3 - USMF...Analiza urinei din 24 de ore Andreea Andronesi, Bogdan Sorohan, Gener Ismail 372 Gena Ismail 375 Gener Ismail Examenul cantitativ al sedimentului urinar 383 Andreea Andronesi,

PDF3 - USMF...Analiza urinei din 24 de ore Andreea Andronesi, Bogdan Sorohan, Gener Ismail 372 Gena Ismail 375 Gener Ismail Examenul cantitativ al sedimentului urinar 383 Andreea Andronesi,

Chimie Analitică şi Instrumentalăamac.md/.../20/CD_Root/data/11-Books/Laboratoria/Chimie.pdf · 2018. 6. 8. · Prefaţă Prefaţă Lucrarea intitulată Chimie Analitică şi Instrumentală

Chimie Analitică şi Instrumentalăamac.md/.../20/CD_Root/data/11-Books/Laboratoria/Chimie.pdf · 2018. 6. 8. · Prefaţă Prefaţă Lucrarea intitulată Chimie Analitică şi Instrumentală

UNIVERSITATEA “ALEXANDRU IOAN CUZA” DIN IAŞI … · Lect.dr. Dan Maftei Universitatea „Alexandru Ioan Cuza” din Iaşi Prof.gr.I, Vasile Sorohan Inspector Şcolar Chimie ISJ

UNIVERSITATEA “ALEXANDRU IOAN CUZA” DIN IAŞI … · Lect.dr. Dan Maftei Universitatea „Alexandru Ioan Cuza” din Iaşi Prof.gr.I, Vasile Sorohan Inspector Şcolar Chimie ISJ

1. INTRODUCERE, MĂRIMI FIZICE, DIMENSIUNI, UNITĂŢI DE ...ns2.islavici.ro/articole/CURS FIZICA si CHIMIE.pdf · Exemplu: putem măsura lungimea cu pasul, palma, liniarul, ruleta,

1. INTRODUCERE, MĂRIMI FIZICE, DIMENSIUNI, UNITĂŢI DE ...ns2.islavici.ro/articole/CURS FIZICA si CHIMIE.pdf · Exemplu: putem măsura lungimea cu pasul, palma, liniarul, ruleta,

Colegiul “Costache Negruzzi “ Iaşicolegiulnegruzzi.ro/_uploads/olimpiade_concursuri/...Sorohan Vasile Chimie Concursul Internaţional „Romanian Master of Matematics and Sciences

Colegiul “Costache Negruzzi “ Iaşicolegiulnegruzzi.ro/_uploads/olimpiade_concursuri/...Sorohan Vasile Chimie Concursul Internaţional „Romanian Master of Matematics and Sciences

E ApaServ în fiecare casä Compania judeteana APA SERV S.A ... de chimie.pdf · E ApaServ în fiecare casä Compania judeteana APA SERV S.A. Nearnt Laborator Analize Apã Potabilã

E ApaServ în fiecare casä Compania judeteana APA SERV S.A ... de chimie.pdf · E ApaServ în fiecare casä Compania judeteana APA SERV S.A. Nearnt Laborator Analize Apã Potabilã

CURS VI - chimie12.weebly.comchimie12.weebly.com/uploads/1/2/2/6/12264090/analiza_spectrala.pdf · Mircea Darabantu CHIMIE ORGANICA an II Ing. CURS-VI ...

CURS VI - chimie12.weebly.comchimie12.weebly.com/uploads/1/2/2/6/12264090/analiza_spectrala.pdf · Mircea Darabantu CHIMIE ORGANICA an II Ing. CURS-VI ...

Proiect CAPACITATI Modernizarea Laboratorului de Fizica ... de chimie.pdf · Proiect CAPACITATI Modernizarea Laboratorului de Fizica Moleculara si Biomoleculara GUVERNUL ROMÂNIEI

Proiect CAPACITATI Modernizarea Laboratorului de Fizica ... de chimie.pdf · Proiect CAPACITATI Modernizarea Laboratorului de Fizica Moleculara si Biomoleculara GUVERNUL ROMÂNIEI

COLEGIUL ,,STEFAN BANULESCU” CALARASI Str. Prelungirea ... didactica chimie.pdf · Mijloace de învățare: sticlărie și aparatură de laborator, substanțe chimice, tablă, fișe

COLEGIUL ,,STEFAN BANULESCU” CALARASI Str. Prelungirea ... didactica chimie.pdf · Mijloace de învățare: sticlărie și aparatură de laborator, substanțe chimice, tablă, fișe

Vasile Sorohan- Culegere Chimie

Vasile Sorohan- Culegere Chimie

ALCHENE, alchine diene - chimie12.weebly.comchimie12.weebly.com/uploads/1/2/2/6/12264090/alchene_alchine_diene… · ReacŃii de oxidare ale alchenelor C C + RCOOH C C O H+, HOH C

ALCHENE, alchine diene - chimie12.weebly.comchimie12.weebly.com/uploads/1/2/2/6/12264090/alchene_alchine_diene… · ReacŃii de oxidare ale alchenelor C C + RCOOH C C O H+, HOH C

Curs EFIM Sorohan 2009 2010

Curs EFIM Sorohan 2009 2010

LISTA PROPUNERILOR DE PROIECTE ELIGIBILE TRANSFER LA ... la operatorul...Tehnologia informatiei si a comunicatiilor, spatiu si securitate 2 PN-III-P2-2.1-PTE-2016-0006 Sorohan Georgeta

LISTA PROPUNERILOR DE PROIECTE ELIGIBILE TRANSFER LA ... la operatorul...Tehnologia informatiei si a comunicatiilor, spatiu si securitate 2 PN-III-P2-2.1-PTE-2016-0006 Sorohan Georgeta

Izomeria compusilor organici - chimie12.weebly.comchimie12.weebly.com/uploads/1/2/2/6/12264090/izomeria.pdf · Clasificareaizomerilor izomeri structurali (izomeri de constitutie)

Izomeria compusilor organici - chimie12.weebly.comchimie12.weebly.com/uploads/1/2/2/6/12264090/izomeria.pdf · Clasificareaizomerilor izomeri structurali (izomeri de constitutie)